This invention generally relates to lead-free machinable alloys and more particularly to a lead-free machinable white manganese bronze alloy which is corrosion-resistant and particularly well-suited for use in food handling equipment.
Copper alloys containing up to five percent by weight lead have been used for many years in constructing equipment for the food industry because they are relatively easy to cast and machine and they withstand the vigorous cleaning to which equipment is subjected in such industries. For example, in the processing of chicken and other meats, the food handling equipment must be cleaned and disinfected daily with bleach solutions. Bleach has a high concentration of chlorine, which is a strong oxidizing agent and therefore very corrosive to aluminum and somewhat corrosive to copper, both of which are found in alloys otherwise desirable for such applications. In the past, the introduction of lead into such aluminum and copper-containing alloys was found to give the alloys a lubricating quality which reduced friction at points in which there was metal-to-metal contact.
Unfortunately, it has now been established that ingestion of even small amounts of lead by human beings can cause health problems. Therefore, it is important to minimize the possibility of introducing lead into foods by eliminating all lead in metal alloys that come in contact with food. Also, when lead-containing alloys are machined, the machine turnings as well as spent lubricants will contain high concentrations of lead. These manufacturing by-products present a danger of environmental pollution and therefore should be eliminated if possible. Indeed, even the casting of lead-based alloys is undesirable since lead vapor released during the casting process can enter into the atmosphere.
Various attempts have been made to provide a lead-free alloy for use in food handling equipment and other applications. Unfortunately, such prior alloys have been undesirable for a number of reasons including shrinkage in casting and increased liquidus and pouring temperatures.